EPSG:9518 - WGS 84 + EGM2008 height

{
  "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
  "type": "CompoundCRS",
  "name": "WGS 84 + EGM2008 height",
  "components": [
    {
      "type": "GeographicCRS",
      "name": "WGS 84",
      "datum_ensemble": {
        "name": "World Geodetic System 1984 ensemble",
        "members": [
          {
            "name": "World Geodetic System 1984 (Transit)",
            "id": {
              "authority": "EPSG",
              "code": 1166
            }
          },
          {
            "name": "World Geodetic System 1984 (G730)",
            "id": {
              "authority": "EPSG",
              "code": 1152
            }
          },
          {
            "name": "World Geodetic System 1984 (G873)",
            "id": {
              "authority": "EPSG",
              "code": 1153
            }
          },
          {
            "name": "World Geodetic System 1984 (G1150)",
            "id": {
              "authority": "EPSG",
              "code": 1154
            }
          },
          {
            "name": "World Geodetic System 1984 (G1674)",
            "id": {
              "authority": "EPSG",
              "code": 1155
            }
          },
          {
            "name": "World Geodetic System 1984 (G1762)",
            "id": {
              "authority": "EPSG",
              "code": 1156
            }
          },
          {
            "name": "World Geodetic System 1984 (G2139)",
            "id": {
              "authority": "EPSG",
              "code": 1309
            }
          },
          {
            "name": "World Geodetic System 1984 (G2296)",
            "id": {
              "authority": "EPSG",
              "code": 1383
            }
          }
        ],
        "ellipsoid": {
          "name": "WGS 84",
          "semi_major_axis": 6378137,
          "inverse_flattening": 298.257223563
        },
        "accuracy": "2.0",
        "id": {
          "authority": "EPSG",
          "code": 6326
        }
      },
      "coordinate_system": {
        "subtype": "ellipsoidal",
        "axis": [
          {
            "name": "Geodetic latitude",
            "abbreviation": "Lat",
            "direction": "north",
            "unit": "degree"
          },
          {
            "name": "Geodetic longitude",
            "abbreviation": "Lon",
            "direction": "east",
            "unit": "degree"
          }
        ]
      }
    },
    {
      "type": "VerticalCRS",
      "name": "EGM2008 height",
      "datum": {
        "type": "VerticalReferenceFrame",
        "name": "EGM2008 geoid"
      },
      "coordinate_system": {
        "subtype": "vertical",
        "axis": [
          {
            "name": "Gravity-related height",
            "abbreviation": "H",
            "direction": "up",
            "unit": "metre"
          }
        ]
      }
    }
  ],
  "scope": "Spatial referencing.",
  "area": "World.",
  "bbox": {
    "south_latitude": -90,
    "west_longitude": -180,
    "north_latitude": 90,
    "east_longitude": 180
  },
  "id": {
    "authority": "EPSG",
    "code": 9518
  }
}

{'crs_wkt': 'COMPOUNDCRS["WGS 84 + EGM2008 height",GEOGCRS["WGS '
            '84",ENSEMBLE["World Geodetic System 1984 ensemble",MEMBER["World '
            'Geodetic System 1984 (Transit)"],MEMBER["World Geodetic System '
            '1984 (G730)"],MEMBER["World Geodetic System 1984 '
            '(G873)"],MEMBER["World Geodetic System 1984 '
            '(G1150)"],MEMBER["World Geodetic System 1984 '
            '(G1674)"],MEMBER["World Geodetic System 1984 '
            '(G1762)"],MEMBER["World Geodetic System 1984 '
            '(G2139)"],MEMBER["World Geodetic System 1984 '
            '(G2296)"],ELLIPSOID["WGS '
            '84",6378137,298.257223563,LENGTHUNIT["metre",1]],ENSEMBLEACCURACY[2.0]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433]],CS[ellipsoidal,2],AXIS["geodetic '
            'latitude '
            '(Lat)",north,ORDER[1],ANGLEUNIT["degree",0.0174532925199433]],AXIS["geodetic '
            'longitude '
            '(Lon)",east,ORDER[2],ANGLEUNIT["degree",0.0174532925199433]]],VERTCRS["EGM2008 '
            'height",VDATUM["EGM2008 '
            'geoid"],CS[vertical,1],AXIS["gravity-related height '
            '(H)",up,LENGTHUNIT["metre",1]]],USAGE[SCOPE["Spatial '
            'referencing."],AREA["World."],BBOX[-90,-180,90,180]],ID["EPSG",9518]]',
 'geographic_crs_name': 'WGS 84',
 'geopotential_datum_name': 'EGM2008 geoid',
 'grid_mapping_name': 'latitude_longitude',
 'horizontal_datum_name': 'World Geodetic System 1984 ensemble',
 'inverse_flattening': 298.257223563,
 'longitude_of_prime_meridian': 0.0,
 'prime_meridian_name': 'Greenwich',
 'reference_ellipsoid_name': 'WGS 84',
 'semi_major_axis': 6378137.0,
 'semi_minor_axis': 6356752.314245179}